Studies show that puberty is associated with decreased insulin action, i.e. insulin resistance. The mechanism(s) responsible for the insulin resistance is not clear. The goals of this project are to characterize how puberty alters the hormonal control of energy metabolism in normal man and to define the mechanisms responsible for it by using the technique of hyperinsulinemic-euglycemic clamp with stable isotope tracers to study glucose, leucine and lipid turnover kinetics in vivo.